The role of chromosomal proteins in maintaining the structure and regulating the function of chromatin is studied. Microinjection of antibodies to histones and nonhistone proteins into the cytoplasm and nucleus of somatic cells and of amphibian oocytes indicate that transcribed regions in the genome contain histones and HMG-17 and that HMG-1 and 2 are found in the cytoplasm of somatic cells and the ooplasm of amphibian oocytes. The large pool of these proteins which bind to single stranded DNA suggests that they are required for chromatin assembly. Polyclonal antibodies to 5 M urea-soluble proteins and monoclonal antibodies to histone H1 degrees have been elicited. The antigenic determinants to which the monoclonal antiH1 degrees bind have been identified. The monoclonal antibodies were used to map the orientation of the molecule in chromatin. Chromatin has been fractionated by immunoaffinity chromatography on sepharose column to which chromosomal protein HMG-17 was covalently bound.